The present invention relates generally to systems for treating semiconductor substrates and, more particularly, to transfer systems for transferring and treating a plurality of substrates simultaneously.
A system of this type is disclosed in U.S. Pat. No. 5,178,639. With this known system the cassettes are arranged in a store in such a way that the wafers are positioned essentially vertically. Via a screw conveyor mechanism, the cassettes containing the wafers, still positioned vertically, are moved in front of a wafer-handling robot, which then transfers, the wafers to a horizontal boat. That is to say the wafers are placed in the vertical position in the boat. The xe2x80x98boatxe2x80x99 is then tilted through a quarter turn and placed on a straight line conveyor. There are a number of reactors along said conveyor and the xe2x80x98boatxe2x80x99 is fed to the relevant reactor as required.
It has been found that, with an installation of this type, if the treatment time in the reactors concerned is shortened, capacity problems arise with the various conveyor means for moving the wafers from the cassette store to the reactors concerned.
The aim of this invention is to perform said transport in an effective manner, as a result of which the capacity of the reactors can be fully utilised even in the case of a relatively short treatment time in the reactors.
This aim is realised with a system as described above which has the characterizing features of claim 1. With a construction of this type the xe2x80x98boatxe2x80x99 will always be in a vertical position, that is to say the wafers will always be in a horizontal position when the xe2x80x98boatxe2x80x99 is handled. The transport can be further optimised by using a carousel in combination with at least two reactors. Moreover, with the construction according to the invention a relatively simple handling robot can suffice. Further simplification can take place if, in addition, the store is designed for receiving the auxiliary containers upright and if the first transfer means comprise a bearing surface for said wafers which extends essentially horizontally. Because the auxiliary containers are now received upright, this means that the wafers are always essentially horizontal.
As the diameter of wafers becomes larger, the spacing thereof in cassettes increases. To be able to maintain the same storage capacity this means that the magazines in which such cassettes are stored become ever higher. If the wafers are taken directly from the cassettes and placed in a xe2x80x98boatxe2x80x99, this means that the wafer-handling robot must be able to move over a great height. This means that an expensive wafer-handling robot is needed because the tolerances of the positioning of wafers are particularly small.
Reference is made to U.S. Pat. No. 5,254,170, in which an installation is described in which the wafers are always positioned horizontally and a wafer-handling installation of this type is used. With the construction according to the present invention it can be assumed that there is a relatively high store for cassettes and the cassettes can be positioned at a uniform level using a relatively simple robot and, starting from this level, can be handled by a wafer-handling robot having a relatively small height range in order to be placed in the xe2x80x98boatxe2x80x99. The height range of the wafer-handling robot is in fact determined by the height of the xe2x80x98boatxe2x80x99.
Compared with the constructions with one reactor combined with one carousel in a single chamber, as disclosed, for example, in U.S. Pat. No. 5,407,449, the system according to the present invention which has been described above makes an appreciable improvement in capacity possible by installing two reactors. Furthermore, as a result of the presence of an intermediate station for both the cassettes and for the xe2x80x98boatxe2x80x99 in the present invention it is possible to allow the carousel in the treatment chamber and the carousel of the wafer storage station to rotate while transferring the wafers from the cassettes into the xe2x80x98boatxe2x80x99 or vice versa. By this means all components of the system can be utilised to the optimum. The construction according to U.S. Pat. No. 5,407,449 does not have this flexibility and the carousel of the treatment chamber and the carousel of the wafer storage station are locked in place while handling the wafers. In percentage terms, the increase in capacity is less when more than two reactors are installed. Furthermore, capacity problems can rapidly arise in one of the conveyor means when there are more than two reactors and when the treatment time is relatively short. It has been found that with the process times most commonly used, which are between 1 and 3 hours, a configuration with two reactors leads to the most optimum utilisation of all components of the system.
Therefore, if there is a need to use more than two reactors it is attractive to site a number of the systems described above alongside one another. That is to say by this means systems which operate independently of one another are produced which can be accommodated within a restricted area. This is in contrast to the construction according to U.S. Pat. No. 5,178,639, in which it is proposed when increasing the number of furnaces simply to place these furnaces alongside one another in a row. In the event of the failure of one of the components which provide for the feed/removal of cassettes and xe2x80x98boatsxe2x80x99 and/or wafer handling the entire system will immediately become inoperative. With the assembly according to the present invention, consisting of at least two systems arranged alongside one another, as described above, systems which function independently of one another are obtained and operational reliability is appreciably improved.
In Netherlands Patent 1 005 410 in the name of the Applicant it is proposed no longer to allow the wafer racks to perform exclusively an up and down movement with respect to the reactor, which in general is set up vertically, but also to use these wafer racks for transport of the wafers through the chamber in which such reactors have been installed. In the Netherlands Patent 1 005 410 it is described that the wafer racks are positioned on a rotary platform and, once they have arrived beneath the furnace concerned, are introduced into the furnace by a special device, the underside of the wafer racks also comprising the closure stop for the underside of the furnace.
With constructions of this type it is always necessary to transfer the wafers from the cassettes in which they are fed/removed into/from the wafer racks.
With installations known to date this transfer took place at the interface between the chamber in which the reactor was installed and the store for the cassettes. That is to say, when the conveyor means for feeding the wafer racks to the reactors are stationary, in a certain position the relevant wafer rack located closest to the requisite robot is loaded or unloaded from or into an associated cassette.
As indicated above, it has been found that for certain treatment processes the capacity of the total installation is no longer determined by the capacity of the various reactors.
The aim of the present invention is to provide an installation with which the capacity can be further increased without enlarging the available floor area. After all, in general an installation of this type will be operated under xe2x80x9cclean roomxe2x80x9d conditions where floor area is particularly expensive.
According to the present invention this objective is achieved in that an intermediate store is arranged between said treatment area and the storage means equipped for receiving said container and in that said transfer means comprise first transfer means for moving said container into and out of said treatment chamber.
According to an advantageous embodiment of the invention, the wafers are not moved directly from the wafer racks to the cassette store but the cassettes are removed from the store and brought into an optimum position for receiving or dispensing the wafers. The capacity can be further increased as a result.
According to a further advantageous embodiment of the invention the intermediate store for the wafer racks, which has been described above, can be closed off with respect to both the reactor chamber and the storage area. A lock operation can be provided by this means.
As already indicated, the reactors can comprise furnaces, but it must be understood that said reactors are able to provide any other treatment of wafers disclosed in the prior art. Such reactors can be arranged such that they operate either horizontally or vertically. Of course, the construction of the associated conveyor means is dependent on this. A horizontally arranged rotary platform has been mentioned above as an example for a reactor which can be vertically loaded/unloaded.